Tropical Rainforest
There are many different ways of classifying tropical rainforests, but essentially
they are forests with a canopy that intercepts more than 70 percent of the sunlight.
Probably the most widely accepted classification system of our local forests is
documented in "The Vegetation of the Humid Tropical Region of North Queensland"
by J.G. Tracey and published by CSIRO 1982. Chakoro Nature Reserve appears on a
vegetation map in this book as vegetation mosaic type 23a, with its
dominant fan palm forest (type 3b) showing up clearly.
A more recent work by Goosem, Morgan and Kemp classifies the Wet Tropics eco-systems
as part of a State-wide process. Using this methodology, Chakoro Nature Reserve contains
elements of types 7.3.1, 7.3.4, 7.3.5, 7.3.6 and 7.11.1
Adjacent to Chakoro Nature Reserve, the rainforest was cleared in the 1960s for banana
production. This area has deep, free-draining, red soil and supported Mesophyl
Vine Forest (types 1a and 2a). This is the classical tropical rainforest with trees
up to 45 metres tall, buttressed trees are common as are woody lianes (vines), epiphytic
ferns (growing on, but not parasitic on, trees) and a ground layer of herbs with
large wide leaves.
The clearing stopped where the red soil becomes shallow and stoney, however the
forest is slowly fighting back and given a few decades to recover from the last
round of logging, it will mature into good forest once again. Cyclones are an unpredictable
threat to the area every summer wet season. During severe cyclones, many trees will
fall or have broken limbs and most leaves will be stripped away. Recovery is quick
so long as there is no fire amongst the debris, but the damage to the crowns of the
tallest trees give the forest its "cyclone scrub" appearance.
Below the red soil slopes the ground becomes boggy, grey clay and the vine forest
merges into fan palm forest, melaleuca forest
and eucalypt and acacia tall, open forest.
Rainforest is reknowned for its bio-diversity which makes
it a very stable, luxuriant eco-system, so people sometimes find it hard to understand
why it is often refered to as being "fragile". The answer lies in the very complexity
that makes it so stable. When rainforest is logged, it is not only the trees which
are disturbed, it is the soil, the leaf litter on the forest floor, birds nests,
mahogany gliders' hollow trees, cassowaries' food supply for their chicks, and so on.
This impact on so many interlocking sub-systems can throw the web of life completely
out of balance. The soil gets exposed to the sun and dries up, stopping the recycling
of nutrients, and the bulk of the nutrients which are locked up in the wood of tree
trunks, is taken away forever. The tree crowns left behind still represent a good
store of nutrients, but they are locked up for the time being, and not available
to help the young saplings to grow and quickly fill in the gaps in the forest canopy.
The species that do well under these circumstances are weeds such as Lantana and Moluccan
Bramble, and tall grasses such as Guinea Grass. These weeds use a technique known
as Allelopathy (literally 'poisoning others') to establish themselves in colonies.
They create chemicals in their roots which they can tolerate themselves, but which
leach into the soil and slow down the growth of other species. Guinea Grass also
has long, rough leaves that swish back and forth in the wind to wear down the tender
growing shoots of rainforest regrowth trees.
The Amethystine Python is one of the forest's most important hunters - this one
has one of my chooks inside him. He is 3.5 metres long and his patterning is perfect
camouflage against the leaves of the forest floor. Can you see his head?
A much smaller snake is the non-venomous Green Tree Snake Dendrelaphis punctulata.
I have seen one of these chase and grab a White-lipped Tree Frog Litoria infrafrenata
by the head and then get stuck because it was just too big to swallow. After a few
minutes the snake let go and slipped away and the stunned frog sat there for a few
minutes enjoying his lucky day.
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